Nitinol alloy design and composition for vascular stents

Abstract

A stent and a delivery system for implanting the stent in a body lumen is disclosed. The stent is made from a superelastic alloy such as nickel-titanium or nitinol, and includes a ternary element in order to minimize the stress hysteresis of the superelastic material. The stress hysteresis is defined by the difference between the loading plateau stress and the unloading plateau stress of the superelastic material. The resulting delivery system has a small profile and includes a sheath covering the stent that has a thin wall.

Description

BACKGROUND OF THE INVENTION[0001]The present invention generally relates to self-expanding endoprosthesis devices, in particular self-expanding intraluminal vascular grafts, generally called stents, adapted to be implanted in a body lumen, such as carotid arteries, coronary arteries, peripheral arteries, veins, or other vessels to maintain the patency of the lumen. These devices are frequently used in the treatment of atherosclerotic stenosis in blood vessels especially after percutaneous transluminal angioplasty (PTA) or percutaneous transluminal coronary angioplasty (PTCA) procedures, with the intent to reduce the likelihood of restenosis of a vessel. Stents are also used to support a body lumen, tack-up a flap or dissection in a vessel, or in general where the lumen is weak to add support. The present invention also relates to an intraluminal vascular graft that can be used in essentially any body lumen.[0002]In expandable stents that are delivered with expandable catheters, such...

AI Technical Summary

Benefits of technology

The present invention is about a stent and delivery system for implanting the stent in a body lumen. The stent is made of a cylindrically-shaped stent with a superelastic alloy that includes a ternary element and has a small stress hysteresis. The delivery system includes a sheath with a distal end and a proximal end, where the stent is disposed inside the sheath at the distal end, and the sheath has a small profile. The stent is designed to perform various mechanical functions within the lumen, all of which are based upon the lower unloading plateau stress. The invention has a reduced delivery system profile for any given level of stent mechanical performance and better flexibility. The superelastic alloy may include binary nickel-titanium alloys or other elements such as palladium, chromium, iron, cobalt, vanadium, manganese, boron, copper, aluminum, tungsten, or zirconium.

Problems solved by technology

The problems with some prior art stents, especially those of the expandable type, is that they are often stiff and inflexible.

Because these stents are so close to the surface of the body they are particularly vulnerable to impact forces that can partially or completely collapse the stent and thereby block fluid flow in the vessel.

Since the prior art stents are plastically deformed, once collapsed or crushed they will remain so, permanently blocking the vessel.

Thus, the prior art stents can pose an undesirable condition to the patient.

Other forces can impact the prior art stents and cause similar partial or total vessel blockage.

Under certain conditions, muscle contractions might cause the prior art stents to partially or totally collapse and restrict blood flow in the vessel in which they are implanted.

In particular, in the stress-strain curve exhibiting loading and unloading of the shape memory alloy material, the applicant suggests using a composition that results in a large difference between the loading and unloading curves, otherwise known as a wide hysteresis.

This can mean that the lumen will be resistant to being crushed by externally applied forces which can be a problem in the case of lumens close to the surface such as arteries in the thigh and neck.

Unfortunately, the greater the difference between the loading and unloading stress plateaus, the stronger the delivery system must be to accommodate any given level of stent performance.

This is a major drawback to conventional superelastic stents and delivery systems when the stent must be delivered through tortuous vessels at remote locations in the human anatomy.

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